It is very common to experience a delayed period after taking the i-pill (levonorgestrel). This medication contains hormones that temporarily alter your menstrual cycle, which frequently causes your period to be early, late, or lighter than usual. While a delay is a normal side effect, no emergency contraceptive is 100% effective. For your peace of mind, I highly recommend taking a home pregnancy test if your period is delayed by more than one week. Please try to relax, as stress can also cause delays.